A024156 Number of integer-sided triangles with sides a,b,c, a<b<c, a+b+c=n that are obtuse.

0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 2, 1, 2, 2, 3, 2, 4, 3, 6, 3, 7, 4, 8, 6, 9, 7, 10, 8, 12, 10, 15, 11, 16, 13, 18, 15, 19, 17, 21, 19, 25, 21, 28, 22, 30, 25, 32, 28, 35, 31, 38, 33, 41, 35, 45, 38, 47, 42, 51, 46, 53, 50, 57, 52, 61, 55, 65, 58, 68, 63, 74, 67, 77, 71, 82, 74, 86, 77, 92, 82, 96, 87

Offset

1,13

Links

Jean-François Alcover, Table of n, a(n) for n = 1..200

Mathematica

r[n_] := Module[{a, b}, Reduce[a>1 && a<b && a + 2b < n && 2(a + b) > n && 2n(a + b) < 2a*b + n^2, {a, b}, Integers]];
a[n_] := Module[{rn = r[n]}, Which[rn === False, 0, rn[[0]] === And, 1, rn[[0]] === Or, Length[rn], True, Print["error: ", n, " ", rn]]];
Array[a, 84] (* Jean-François Alcover, Mar 01 2019 *)

Crossrefs

Cf. A024154, A024155.

Sequence in context: A127682 A127685 A127687 * A241316 A241312 A075989

Adjacent sequences: A024153 A024154 A024155 * A024157 A024158 A024159

Keyword

nonn

Author

Clark Kimberling

Status

approved